Question 133103
Given: {{{(x-4)/(x-8) - (x+1)/(x+8) + (x-72)/(x^2 -64) }}}

Simply:
In order to combine the three terms, you need to have a common denominator. In this case, the least common denominator is {{{(x^2 -64)}}}

So multiply the first term by {{{(x+8)/(x+8)}}} and the second term by {{{(x-8)/(x-8) }}}  (note both values are equal to 1.

This yields:
{{{(x-4)(x+8)/(x-8)(x+8) - (x+1)(x-8)/(x+8)(x-8) + (x-72)/(x^2 -64) }}}

Now multiply out (expand) the numeratiors to get:
{{{((x^2 + 4x -32) - (x^2 -7x -8) +(x-72))/((x-8)(x+8))}}} 

Collect terms in the numerator to get:
{{{(12x -96)/((x-8)(x+8))}}} 
{{{(12(x -8))/((x-8)(x+8))}}} 
{{{(12)/((x+8))}}}